Wireless terminals for communication such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNodeB (eNB), NodeB, B node, Base Transceiver Station (BTS), or AP (Access Point), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for terminals. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE is controlled by the radio base station.
Local service clouds in a base station are demanded to optimize a backhaul network. In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between a core network or a backbone network and small sub-networks at the edge of the entire hierarchical network, such as e.g. between a base station and a radio network controller.
Cloud computing in general may be portrayed as a synonym for distributed computing over a network, with the ability to run a program or application on many connected computers at the same time. It specifically refers to a Computing hardware machine or group of computing hardware machines commonly referred as a server connected through a communication network such as internet, intranet, Local Area Network (LAN) or Wide Area Network (WAN) and Individual user or users as well as base stations who have permission to access the server can use the server's processing power for their individual computing needs like to run an application, store data or any other computing need alike.
The local service clouds in a base station enable local functions to be added to the base station such as e.g. data compression, tunneling, and Forward Error Correction (FEC) function to enhance the backhaul when internet is used as a backhaul. Further examples are local applications, e.g. the backhaul network usually has bottlenecks that will limit the performance of the applications at the core network sites. Applications running in the local service cloud at the base station site will fully utilize the radio link.
One of the problems to enable application execution for a UE at a base station site is the local breakout of traffic from the Radio Bearers (RBs) to the local application at the local service cloud. The RBs will be further explained below. The local breakout is usually realized by a classifier which inspects passing data traffic. Based on the inspected passing data traffic, the classifier classifies the data traffic e.g. based on Differentiated Services Code Point (DSCP) and/or 5-tuple. A 5-tuple refers to a set of five different values related to a Transmission Control Protocol/Internet Protocol (TCP/IP) connection. The 5-tuple includes a source IP address/port number, destination IP address/port number and the protocol in use. Based on the classified data traffic, the classifier then routes traffic classified as local application traffic through a specific interface between the base station and the local service cloud.
In the end-to-end traffic in this example where one end is the UE and the other end is the server where the application/service is running, the non-local traffic may be tunneled within a GTP-tunnel. The classification is made on the end-to-end traffic instead of the tunnel header. This is known for people skilled in 3GPP-architecture.
There are many bearers, i.e. GTP-tunnels to a base station and there are many base stations. Due to the mobility of the UEs the UEs connected to a base station is varying over-time i.e. one UE moves its connection between many base stations. The specific set of UEs connected to one base-station is therefore varying over time. A RB is an association for the base-station to know how and to which UE the traffic should be sent to. The RB has two directions, one uplink direction which is the traffic from the UE to the base station, and one downlink direction which is the traffic from the base station towards the UE.
The traffic in the uplink can easily be classified and broken out, i.e. routed to the local service cloud. If any kind of tunnel header is used for a broken out packet, such as a GTP tunnel header, it is stripped off before the packet is delivered to the application server in the local service cloud, such that the application server only receives the native end-to-end packets.
An IP address is allocated to a UE when a default bearer is activated. The IP address allocated for the default bearer is used for the dedicated bearers within the same Packet Data Network connection. A major problem in this scenario is that the UE's IP address cannot be guaranteed to be unique. Several UEs may be allocated the same private IP address. This is most critical when the traffic shall be routed downlink and the traffic from the local service cloud shall be inserted, i.e. broken in, into a RB belonging to the correct UE. There are many UEs and downlink RBs to select between and a native IP packet which is sent from the local service cloud has no relation to UE identities or RB identities. The lack of guaranteed IP address uniqueness is a problem also in the uplink, since the traffic from different UEs may interfere, i.e. be mixed with each other and confuse the application servers in the local service cloud. The applications in the local service cloud require different UE IP addresses and an operating system uses the UE IP addresses and port numbers as identifiers of the application sessions.
Note also that one UE may use several servers in the local service cloud such that traffic from those servers must be broken in and routed to the same UE.
An Evolved Packet System (EPS) is a central network portion of the UMTS LTE mobile communication system. An EPS primarily transfers packet data between edge networks and the radio access network. In an EPS network a bearer between a UE and a Packet Data Network (PDN) Gateway (PGW) is denoted “EPS bearer”. In between the UE and the PGW the EPS bearer traverses an eNodeB (eNB) and a Serving Gateway (SGW). The parts of the EPS bearer between the PGW and the SGW and between the SGW and the eNB are realized through GTP tunnels. The part of the EPS bearer between the eNB and the UE is realized through radio interface user plane protocols and is denoted Radio Bearer (RB). An EPS bearer is bidirectional, i.e. it has both an uplink and a downlink direction.
A solution is to handle the problem of non-unique UE addresses by introducing Network Address Translation (NAT) between the UE and the local service cloud.
NAT
Primarily NAT was introduced to the world of Information Technology (IT) and networking due to the lack of IP addresses. When computers and servers within a network communicate, they need to be identified to each other by a unique address, in which resulted in the creation of a 32 bit number, and the combinations of these 32 bits would accommodate for over 4 billion unique addresses, known as IP address. This was named IPv4, and although over 4 billion addresses sounds a lot, it really is not considering how fast the world of computers and the internet has grown.
To circumvent this problem, a temporary solution was produced known as NAT. NAT resulted in two types of IP addresses, public and private. A range of private addresses were introduced, which anyone could use, as long as these were kept private within the network and not routed on the internet.
NAT allows the use these private IP address on the internal network. So within a private network a unique IP address is assigned to all computers, servers and other IP driven resources in the private network. Another company can use the same private IP addresses as well, as long as they are kept internal to their network. So two companies may use the same range of IP addresses but because they are private to their network, they are not conflicting with each other.
However when internal hosts need to communicate with a public network such as the Internet the public address is used. This address is a routable public address everyone can see, which would represent the network gateway of the user. This public address would be unique; no one else would use this address.
A problem with a NAT solution is that the NAT:ed UE-addresses are locally unique. The uniqueness will not hold in mobile scenarios, where movements may cause the UE to connect to a new local service cloud in which the NAT:ed IP address is not unique.
Another problem with the NAT solution is that a NAT includes a state that makes it difficult to interwork with mobility. The connectivity is broken when the mobile is handed over to another base-station.
A yet further problem with the NAT solution is that some applications may not work equally well when there is a NAT in a path. Here the path refers to the connection between the two ends of a communication.
The lack of uniqueness of the UE IP address is a consequence of 3GPP architecture where the core network decides and allocates an IP address range to each Access Point Name (APN). The same IP address range or overlapping ranges may be allocated to different APNs, such that IP addresses can be reused between APNs.
An APN identifies a PDN that a mobile data user wants to communicate with. In addition to identifying a PDN, an APN may also be used to define the type of service, such as e.g. connection to a wireless application protocol server, multimedia messaging service (MMS), which is provided by the PDN. APN is used in 3GPP data access networks, e.g. General Packet Radio Service (GPRS), and Evolved Packet Core (EPC).